Therapies for preventing the onset or progression of neonatal pulmonary hypertension have received little attention and have largely targeted the nitric oxide pathway. Our findings indicate that an interplay between the prostanoid and NADPH oxidase signaling pathways plays a key role early in the development of chronic hypoxia-induced neonatal pulmonary hypertension. Our overall hypothesis is that within 3 days exposure to hypoxia, disruptions in prostanoid and NADPH oxidase signaling occur which mediate changes in smooth muscle cell (SMC) reactive oxygen species (ROS) production and voltage-gated K+ (Kv) channel function. These changes create a feed-forward process that self-perpetuates vascular dysfunction and is amplified when hypoxia is extended to 10 days. The specific hypotheses are: chronic hypoxia (1) activates prostanoid and NADPH oxidase pathways leading to elevated constrictor prostanoid production and ROS generation in SMCs of pulmonary resistance arteries (PRAs) which in turn (2) impairs SMC Kv channel function, causing SMC membrane (Em) depolarization and elevated cytosolic calcium concentration. Specific Aim 1 will determine the effect of 3 or 10 days hypoxia on (a) relative contributions of prostanoid and NADPH oxidase signaling pathways to ROS production and aberrant PRA responses (using cannulated PRA, lucigenin- derived chemiluminescence, oxidant-sensitive fluorescent dye, and cultured SMC techniques) and (b) amounts (immunoblot), activity (enzyme assays) and predominant cellular locations (immunohistochemistry) of NADPH oxidase and superoxide dismutases. Key findings will be validated with in vivo studies. Specific Aim 2 will evaluate the effect of 3 or 10 days hypoxia on (a) contribution of Kv channels to vascular tone (cannulated arteries) (b) SMC Em (microelectrode) (c) SMC Ca2+ (fluorescence) and (d) Kv channel amounts (immunoblot). Our findings will provide new information needed to devise therapies to intervene with the development of pulmonary hypertension in infants with conditions associated with chronic hypoxia. Relevance: Pulmonary hypertension is a well recognized complication of infants with a variety of lung and heart disorders. Currently there are few good options for treating these infants. The goal of this project is to help us understand why infants develop pulmonary hypertension, determine what happens in the lung blood vessels during disease development, and develop treatments for this disease.